Mechanical assemblies often use fasteners and typically blind rivets to secure one or more components together in a permanent construction. Blind rivets are preferred where the operator cannot see the blind side of the workpiece for instance where the rivet is used to secure a secondary component to a hollow box section. Also they are preferred where a high volume of assemblies are being produced as there are advantages to be gained from increased assembly speeds and productivity compared with threaded or bolted joints.
One of the disadvantages of a blind rivet setting to a hollow box section is that the blind side set end of the rivet cannot be visually inspected for a correctly completed joint. This is especially relevant where there are a number of blind rivets used and these are of a multiplicity of different sizes in both diameter and length. In addition, there could be occasions where assembly operators are inexperienced or the arrangements of rivets are complex. Further, it is possible that rivets are incorrectly installed or perhaps not installed at all. To inspect assemblies after completion is not only expensive and unproductive and in some instances, it is virtually impossible to identify if the correct rivet has been used in a particular hole. A further consideration can be that modern assembly plants are using increasing numbers of automative rivet placement and setting tools where there is an absence of the operator.
The current monitoring of a rivet during the setting process has been limited to the use of two classes of methods. The first method employs the use of a hydraulic pressure transducer, which measures working fluid pressure within the tool. This current method is limited to use in detecting fluid pressure alone. The second method uses a “load cell” mounted linear to the tool housing. This option uses equipment, which is considerably larger and has limited field capability as a result. Typically, the second method additionally uses a LVDT to measure the translations of the various moving components.
In accordance with the present invention, a system is provided that will continually monitor the setting process, the numbers of rivets set and the correctness of setting and to identify if there are small but unacceptable variations in rivet body length or application thickness. In addition, because assembly speeds are increasing, it is an advantage to identify incorrect setting almost immediately instead of a relatively long delay where complex analysis of rivet setting curves is used. Other fasteners such as blind rivet nuts (POP®nuts), self-drilling self-tapping screws or even specialty fasteners such as POP®bolts can be monitored but for the purposes of this description, blind rivets are referred to as being typical of fasteners used with this monitoring system.
There are a variety of different types of tools, both manual and powered, that are used to set pull-type or swage-type fasteners. For industrial production, it is desirable to use a power tool that may have an air/hydraulic or hydraulic/hydraulic power assist to pull the mandrel stem. This facilitates the rivet setting operation.
To overcome the disadvantages of the prior art, a fastener set monitoring system is provided which has a sensor that measures motor current, torque or RPM within a tool component. In this regard, the system utilizes sensors to monitor variations in current or torque in a servomotor used to drive a hydraulic pump. These measured currents or torque are compared to a data array or function which represents data conforming to an acceptable fastener set. Various techniques are provided to analyze the measured data with respect to the tolerance bands to determine if a particular river set is acceptable.
In one embodiment, a fastener setting tool having a hydraulically driven pulling head for engaging and setting a fastener and upon actuation is provided. The rivet setting tool has a hydraulic pressure source coupled to the riveting head and an intensifier operably coupled to the hydraulic pressure source. A servomotor is coupled to a pump to form the hydraulic pressure source that is configured to apply fluid pressure to cause the setting of the fastener.
In another embodiment, a fastener setting tool is provided having a pulling head which has a hydraulic pressure source coupled to a fastener engaging member. The hydraulic pressure source is formed of a pump, which is driven by a servomotor. A sensor is used to measure current or torque within the servomotor over a fastener set event. These measured torque or current values are compared in a time or displacement domain to tolerance bands formed about median current or torque versus time or displacement data. Various techniques are provided to analyze the measured data with respect to the tolerance bands to determine if a particular river set is acceptable.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.